1. Technical Field
The present disclosure relates to a communication apparatus, a terminal station, and a communication method.
2. Description of the Related Art
Task Group ax of IEEE (the Institute of Electrical and Electronics Engineers) 802.11 Working Group has been developing the IEEE 802.11ax (hereinafter referred to as “11ax”) technical specification, which is a successor to 802.11ac. OFDMA (Orthogonal frequency-division multiple access) based random access (RA: Random Access) is likely to be introduced into 11 ax.
An access point (also referred to as a “base station”) transmits a random access control signal (hereinafter referred to as “TF (Trigger frame) -R”) to a plurality of terminals (also referred to as terminal stations or “STAs (Stations)”) that the access point accommodates. TF-R includes RU information indicating a transmission frequency resource for random access (hereinafter referred to as a “Resource unit (RU)”). A terminal that transmits a UL response signal (also referred to as a “UL (Uplink) response frame”) through random access selects one of the plurality of random access RUs indicated by the RU information for random access (RA RUs) included in TF-R at random and transmits a UL response signal by using the selected RU (refer to, for example, IEEE 802.11-15/0875r1 “Random Access with Trigger frames using OFDMA”).
For the 11ax, various random access applications are being studied. Two applications of random access which have been studied are described below.
The first use of random access is to notify the access point of uplink transmission buffer information (also referred to as “Buffer Status Information”) (refer to, for example, IEEE 802.11-15/0843r1 “UL MU Random Access Analysis”).
The access point allows a plurality of terminals to perform random access by TF-R. A terminal having uplink data (UL Data) in the transmission buffer randomly selects one RU from among the RA RUs specified by the TF-R. Thereafter, the terminal transmits a UL response signal including the transmission buffer information to the access point by using the selected RU. The access point can get to know the transmission buffer state of each of terminals on the basis of the transmission buffer information received through random access and, thus, can efficiently schedule the UL Data after random access.
The second use of random access is to transmit an uplink signal by OFDMA even when a terminal operating in a power saving mode (also referred to as a “Power Saving (PS) terminal”) returns from the power saving state, and the access point does not know that the terminal holds uplink data in the transmission buffer. This use can prevent a decrease in transmission efficiency caused by a plurality of terminals performing uplink transmission separately as a single user (SU) (refer to, for example, IEEE 802.11-15/1107r0 “Power Save with Random Access”).